Henri Bergson's general observations related to when laughter is most likely to appear and thrive:
The comic is strictly human. When laughter is directed at non-humans, we may laugh, but only because we have detected some human attitude or expression.
Laughter has no greater foe than emotion. Emotional states like pity, melancholy, rage, etc. make it difficult for us to find humour in the things we might otherwise have laughed at. But humour also appears to serve as a coping mechanism in the face of tragedy or misfortune.
Laughter seems to require an echo. It is used in the context of social bonding.
Our image of the Victorians is shaped by the photographs we see in history books – stern, austere and relentlessly severe. Yet there was a playful side to our 19th-century ancestors, and Lloyd Llewellyn-Jones has the proof. Here he introduces a selection of portraits that show the sitters doing something entirely unexpected: smiling
The picture shows a family who is captured a bit earlier than expected, fact that allows us to see everybody's natural laughter. This is what used to be known as 'Gigglemug' or 'habitually smiling face'.